Boolean Modifier making original object disappear
The problem is that one of your two objects to be used in a Boolean operation is the combination of two joined objects. You don't want that. You want only one object being Booleaned with only one other object. You can fix this simply by separating the joined objects (go into Edit mode, press p for the Separate menu, and then choose to separate by Loose Parts), then  Boolean those two newly separated objects together in Object Mode with a Boolean Union operation. Doing this will make the two previously unjoined objects truly one object, which they actually weren't before. After doing that, you can attempt your Boolean operation mentioned above, and it is very much more likely to work.